It's a common thought behind many fan theories that seemingly unrelated films actually take place alongside each other. Fans love to talk about the connectivity between director Quentin Tarantino's films or the individual bleak futures of Black Mirror, it's even a long-thought theory that all of the Pixar movies take place in the same "universe." A new theory has cropped up that sounds completely insane when you just say it out loud but there's actually some compelling points as noted by the author. The two franchises that they posit actually co-exist? The 1980s horror-comedy series Ghostbusters, and JK Rowling's young-adult fantasy series, Harry Potter.
As written by /u/Exitium31 in the /r/FanTheories subreddit, the two films can seemingly exist alongside each other with very little interference to the continuity of either franchise. They write: "I interpret that Ghostbusters is when muggles start to discover magic by scientific ways instead of wizards who were born with it. The proton packs, the neutrino wands and the particle accelerator are just technological wands that the main characters accidentally discovered while making ghost trapping technology."
/u/Exitium31 also theorized that the villain of Ghostbusters, Gozer the Destructor, was a witch that conned the entire "Cult of Gozer" into believing she was a god, constructing the 550 Central Park West building as a "Primitive Horcrux" to bring them back like Voldemort famously does in the series. In addition they theorize that Vigo the Carpathian from Ghostbusters II used the painting of himself from the film as a Horcrux as well.
The major crux of the theory though is in how "The Wizarding World" responds to the events of the film as /u/Exitium31 theorizes that Walter Peck (the human antagonist of Ghostbusters) is actually himself a Wizard and has been sent to clean up the situation. Furthermore they even take the events of 2016's Ghostbusters reboot into account with a Potter-explanation to connect all the dots. You can read the full theory and its very convincing explanations by clicking here.
Hilariously, the top comment for the theory reads: "What pisses me off is the fact that no matter what angle I think about it from, I can’t find a way to refute this dumbass (albeit well thought out) theory."
The next entry in the Ghostbusters franchise will be the upcoming Ghostbusters: Afterlife. Originally set to be released on July 10 of this year, the new film from director Jason Reitman, was delayed until March 19, 2021. Sadly we'll have to wait until then to see if this theory still holds water.